Technical Abstract:
A procedure, based on immunomagnetic capture and time-resolved fluorescence, was developed to detect Escherichia coli O157:H7 and Salmonella Typhimurium in ground meats and fresh sprouts. After a brief enrichment period, streptavidin coated magnetic beads conjugated with biotin-labeled specific anti bacteria antibodies were used to capture targeted pathogenic bacteria. The bacteria were, at the same time, also labeled by a non-fluorescent, lanthanide-(Eu or Sm)-tagged bacterial antibodies. The sandwiched bacterial complexes were then concentrated using a magnetic particle concentrator and washed to remove other solution components. Upon addition of an enhancement buffer, the La-labels were then released from the antibodies and chelated to nitrilo-triacetic acid (NTA) and trioctylphosphine oxide (TOPO) to form highly fluorescent La-(2-NTA)3(TOPO)2-3 micellar complexes. Measured intensities of delayed fluorescence associated with Eu and Sm complexes were used to estimate the original concentration of E. coli O157:H7 and Salmonella Typhimurium spiked in foods, respectively. The results indicated this method is able to detect ~ 1 to 4 CFU/g of the bacteria individually or in-pair after a brief enrichment for four to six hours at 37 oC. Specificity studies indicated that the approach exhibited no or limited cross reactivity between tested bacteria and with other non-pathogenic bacteria, e.g., E. coli K-12 in foods. The developed approach may be used as a rapid screening procedure for the detection of pathogenic E. coli and Salmonella in foods.